This research program is designed to assess experimentally the manner and extent to which environmental factors either contribute to or determine the behavioral effects of abused drugs. Studies will be conducted with squirrel monkeys, pigeons and rabbits under a wide range of conditions where the behavioral performances are orderly, stable and reproducible and where both the previous and current conditions are systematically manipulated. The predominant emphasis will consist of analyzing specifically the role of: 1) prior behavioral experience, 2) prior drug history and 3) the current environmental setting as these factors either singly or together determine changes in behavior produced by drugs of abuse. These studies will contribute essential information on behavioral, environmental and pharmacological determinants of the effects of abused drugs and will aid in providing the basis for a more complete understanding of factors determining the effects on behavior of drugs of abuse.